Chemical pulping and bleaching in an enclosed reaction zone,by reduction of chlorate

ABSTRACT

A PROCESS FOR THE TREATMENT OF CELLULOSIC MATERIAL IN SUBDIVIDED FORM INCLUDING THE STEPS OF FIRSTLY PROVIDING AN ENCLOSED REACTION ZONE FOR THE TREATMENT OF THE CELLULOSIC MATERIALS; SECONDLY PROVIDING A REACTANT LIQUOR PHASE IN THE REACTION ZONE; THIRDLY PROVIDING A SUPERPOSED GAS PHASE OVER THE REACTANT LIQUOR IN THE REACTION ZONE; AND FOURTHLY AGITATING THE CELLULOSIC MATERIAL IN THE ENCLOSED REACTION ZONE. THE IMPROVEMENT INVOLVES USING AS THE REACTANT LIQUOR PHASE, AN AQUEOUS LIQUOR COMPRISING A LIQUOR SOLUBLE CHLORATE AND A REDUCING AGENT FOR THE CHLORATE, THE REDUCING AGENT BEING PRESENT IN 0.1 TO 2.0 MOLAR EXCESS BASED UPON THE AMOUNT OF CHLORATE USED. BECAUSE OF THE SERIES OF STEPS CARRIED OUT AND THE PARTICULAR COMPOSITION OF THE REACTANT PHASE, THE GAS PHASE SUPERPOSED OVER THE REACTANT LIQUOR IN THE ENCLOSED REACTION ZONE CONTAINS EVOLVED CHLORINE DIOXIDE AND/OR CHLORINE THUS PREVENTING ANY ENCRUSTATION WHICH MAY FORM ON THE OUTER WALLS OR SURFACES OF THE CELLULOSIC MATERIALS.

FIPSEU? CHEMICAL PULPING AND BLEACHING IN AN ENCLOSED REACTION ZONE, BYREDUCTION OF CHLORATE Gothe Oscar Westerlund and Kin Seto, Vancouver,British Columbia, Canada, assignors to Chemech Engineering Ltd.,Vancouver, British Columbia, Canada No Drawing. Filed July 7, 1967, Ser.No. 651,712 Claims priority, application Canada, Feb. 28, 1967,

Int. (:1. 1521c 3/06 US. Cl. 162-64 22 Claims ABSTRACT OF THE DISCLOSUREA process for the treatment of cellulosic material in subdivided formincluding the steps of firstly providing an enclosed reaction zone forthe treatment of the cellulosic materials; secondly providing a reactantliquor phase in the reaction zone; thirdly providing a superposed gasphase over the reactant liquor in the reaction zone; and fourthlyagitating the cellulosic material in the enclosed reaction zone. Theimprovement involves using as the reactant liquor phase, an aqueousliquor comprising a liquor soluble chlorate and a reducing agent for thechlorate, the reducing agent being present in 0.1 to 2.0 molar excessbased upon the amount of chlorate used. Because of the series of stepscarried out and the particular composition of the reactant phase, thegas phase superposed over the reactant liquor in the enclosed reactionzone contains evolved chlorine dioxide and/or chlorine thus preventingany encrustation which may form on the outer walls or surfaces of thccellulosic materials.

This invention relates to the treatment of cellulosic materials insubdivided form. In one aspect, it relates to the pulping and/orbleaching of wood chips or sawdust. In another aspect, it relates to thedelignification and subsequent 'bleaching of lignocellulosic fibrousmaterials.

It is now well known that both chlorine gas and chlorine, dioxide areeffective agents both for the delignification of cellulosic materialsand for the treatment of unpulped wood materials. (See U.S. Patent No.1,843,467 issued Feb. 2, 1932 to J. Traquair et al.)

One known process for bleaching of wood pulp involves preoxidizing thepulp fibers with chlorine dioxide. (See a paper by Singh and Andrews,delivered at the International Pulp & Paper Conference, Murray Bay,Quebec, June 22-25, 1965.) Another known procedure involves the additionof chlorine dioxide to the chlorination stage in a wood pulp bleachingprocess. (See a paper by Rapson and Anderson, delivered at theInternational Pulp & Paper Conference, Murray Bay, Quebec; also CanadianPatent No. 552,007 issued Jan. 21, 1958 to Stone and Matarese.)

Another process heretofore suggested involved the addi tion of chlorateat the chlorination stage of a wood pulp bleaching procedure, allegedlyto produce stronger pulp. (See US. Patent No. 2,903,326 issued Sept. 8,1959 to I. B. Heitman and Canadian Patent No. 586,838 issued Nov. 10,1959 to J. B. Heitman.)

Another process comprises bleaching a cellulosic material using a firstchlorination stage, followed by several stages using hypochlorite and/orchlorine dioxide as subsequent alkali treating and bleaching stages.

Another process suggested was a low temperature disincrustationprocedure involving impregnation of fibrous materials with chlorateandthen reacting the moist material with gaseous hydrogen chloride. (SeeCanadian Patent No. 546,718 issued Sept. 24, 1957 to Ladislav I. Rys.)

Another process suggested was a delignification of ice pulping materialwith a chlorate employing a catalyst for the reduction reaction. (SeeCanadian Patent No. 550,735 issued Dec. 24, 1957 to Paola Marpillero.)Another similar procedure in the preparation of cellulose involvesemploying a catalyst in the chlorate solution. (See Canadian Patent No.283,573 issued Sept. 25, 1928 to Arthur Franz.)

Yet another process involves bleaching cellulosic materials employingboth a chlorine generator and a chlorine dioxide generator inconjunction with the bleaching stages. (See Canadian Patent No. 452,351issued Nov. 2, 1948 to Harry N. Tatomer.)

However, it was reported by Rapson (TAPPI 42, 642- 49) that activatedchlorate failed to result in desirable advantages in the bleaching ofpulp when compared to chlorine dioxide.

An object of one broad aspect of this invention is the provision of animproved cellulosic material treating procedure.

An object of another aspect of this invention is the provision of apulping process which can yield high grade pulp when applied to variouswood species.

An object of yet another aspect of this invention is the provision of aprocess which may be controlled to yield either a partially bleachedwood pulp or a fully bleached wood pulp.

An object of yet another aspect of this invention'is the provision of aprocess which may be used as a secondary pulping process.

An object of still another aspect of this invention is the provision ofa process for the delignification of lignocellulosic materials.

An object of a further aspect of this invention is the provision of aprocess for the bleaching of cellulosic materials.

An object of yet a further aspect of this invention is the provision ofa one step process for the pulping and bleaching of wood in subdividedform.

An object of yet another aspect of this invention is the provision of amultistep process for the pulping of wood in sub-divided form and thesubsequent further bleaching of the so-produced wood pulp.

An object of an ancillary aspect of this invention is the provision of aprocess which may be used for the pulping of wood in sub-divided form,while permitting the recov cry of chemicals and products from thepulping solution.

By one broad aspect of this invention a process is pro vided for thetreatment of cellulosic materials in subdivided form which comprises thesteps of (1) providing an enclosed reaction zone; (2) providing areactant liquor phase in the reaction zone; (3) providing a superposedgas phase over the reactant liquor in the reaction zone; and (4)agitating cellulosic material in the reaction zone; wherein (a) thereactant liquor phase comprises an aqueous liquor comprising a watersoluble chlorate and a. reducing agent for the chlorate, the reducingagent being present in 0.1 to 2.0 molar excess based on the amount ofchlorate; and (b) the gas phase containing evolved chloride dioxide and/or chlorine.

In a preferred aspect of the invention the agitation step is conductedat a temperature of less than C. at pressures between atmospheric and upto 11 atmospheres and a pH of less than 4.

The reducing agent may be acetic acid, hydrochloric acid, sulfuric acid,phosphoric acid or nitric acid.

In one preferred embodiment the reactant liquor phase comprises anaqueous liquor comprising a water soluble chlorate, a water solublechloride and an acid reducing agent for the chloride which is aceticacid, hydrochloric acid, sulfuric acid, phosphoric acid or nitric acid,

In another embodiment the reactant liquor comprises a water solublechlorate, an organic reducing agent which is either oxalic acid ormethanol and an acid. reducing agent for the chlorate which is aceticacid, oxalic acid, hydrochloric acid, sulfuric acid, phosphoric acid ornitric acid.

By yet another embodiment of the invention, the reactant liquor phasecomprises an aqueous liquor comprising a water soluble metal chlorate,sulfur dioxide, and an acid reducing agent for the chlorate which isacetic acid, hydrochloric acid, sulfuric acid, phosphoric acid or nitricacid.

Basically, then, this invention resides in the use, as a pulping, orbleaching or delignifying liquor, of a solution of a reducible chlorateand a reducing agent for the chlorate, whereby to form chlorine dioxide,in situ. There are many such procedures for converting chlorate tochlorine dioxide which are within the scope of the present invention.Among them are the following non-limiting examples:

(A) REDUCTION OF A METAL CHLORATE WITH AN ACID- Many metal chlorates areuseful in such procedure. Among the metal chlorates which are within thescope herein are the chlorates of e.g. ammonium, sodium, calcium,potassium, lithium and magnesium. It is preferred that the metalchlorate be a water soluble metal chlorate, e.g. an alkali metalchlorate, preferably sodium chlorate.

Among the acids which may be used in this procedure are organic acids,e.g. acetic acid and inorganic acids, e.g. hydrochloric acid, sulphuricacid, phosphoric acid, and nitric acid. Particularly preferred ishydrochloric acid.

A particularly advantageous procedure is that described and claimed inCanadian patent application Ser. No. 972,150, represented by thefollowing equations:

NaClO +2HCl ClO /2Cl +NaCl+H O (l) or at higher acidity;

NaClO 6HCl 3Cl +NaCl+ 3H O (2) (B) REDUCTION OF A METAL CHLORATE WITH ANACID IN THE PRESENCE OF A METAL CHLORIDE Many metal chlorates are usefulin such procedure. Among the metal chlorates which are within the scopeherein are the chlorates of e.g. sodium, potassium and calcium. It ispreferred that the metal chlorate be a water soluble metal chlorate,e.g. an alkali metal chlorate, preferably sodium chlorate.

Among the acids which may be used in this procedure are organic acids,e.g. acetic acid and inorganic acids, e.g. hydrochloric acid, sulphuricacid, phosphoric acid, and nitric acid. Particularly preferred issulphuric acid.

Among the metal chlorides which are within the scope herein are thechlorides of e.g. sodium, potassium, calcium, magnesium and ammonium. Itis preferred that the metal chloride be water soluble, e.g., an alkalimetal chlo ride, preferably sodium chloride.

A particularly advantageous procedure is disclosed and claimed inCanadian Patent No. 452,351 issued Nov. 2, 1948 to H. N. Tatomer,represented by the following equation:

(C) REDUCTION OF A CHLORATE WITH AN ORGANIC REDUCING AGENT IN THE PRES-ENCE OF AN ACID Many metal chlorates aer useful in such procedure. Amongthe metal chlorates which are within the scope herein are the chloratesof e.g. sodium, potassium, calcium, magnesium and ammonium. However,sodium chlorate is preferred.

Among the acids which may be used in this procedure are organic acids,e.g., acetic acid and oxalic acid and inorganic acids, e.g. hydrochloricacid, sulphuric acid, phosphoric acid, and nitric acid. Particularlypreferred is sulphuric acid.

Among the organic reducing agents which are within the scope herein aree.g. methanol, and oxalic acid. Particularly preferred is methanol.

A particularly advantageous procedure is disclosed and claimed inCanadian Patent No. 434,213 issued Apr. 16, 1946 to C. A. Hampel et al.represented by the following equation:

(D) REDUCTION OF A METAL CHLORATE WITH SULPHUR DIOXIDE IN THE PRESENCEOF AN A-CID Many metal chlorates are useful in such procedure. Among themetal chlorates which are within the scope herein are the chlorates ofe.g. sodium, potassium and calcium. It is preferred that the metalchlorate be a water soluble metal chlorate, e.g. an alkali metalchlorate, preferably sodium chlorate.

Among the acids which may be used in this procedure are organic acids,e.g. acetic acid and inorganic acids, e.g. hydrochloric acid, sulphuricacid, phosphoric acid, and nitric acid. Particularly preferred issulphuric acid.

A particularly advantageous procedure is that disclosed and claimed inCanadian Patent No. 533,803 issued Nov. 27, 1956 to F. H. Dolerepresented by the following equation:

H2504 2NnClO3+SOz 2CIOz-I-NMSO4 A particularly preferred reagentchlorate liquor is the product produced by the electrolysis ofchlorides. While the chloride may be any water soluble metal chloride,for example sodium, potassium, calcium and magnesium, it is preferredthat the chloride be sodium chloride. The reagent liquor Will thencontain NaClO NaCl, NaOCl, and HOCl. It may also contain dichromate ifit is not treated to recover that compound.

The process herein described may be carried out in one step or inseveral stages. In addition it may be conducted as a batch process or asa continuous process.

It has been found that the size of the wood chips significantly affectedthe treatment time required for pulping. As the size of the wood chipsincreased from 2 mm. thickness x 4 mm. width x 6 mm. length to 3 mm.thickness x 12 mm. width x 25 mm. length, it was found that the pulpingtime, under similar conditions of pulping reagent and reactiontemperature, was increased from 10 to 30 times.

The following examples are given to illustrate aspects of the presentinvention. In all cases, the reaction vessel was a laboratory combineddigester and bleaching apparatus comprising a 1 inch diameter glasstube, 24 inches long.

Example I Wood chips were immersed in a chlorate electrolytic cellselectrolyte containing up to:

650 g.p.l. NaClO 150 g.p.l. NaCl,

3 g.p.l. total NaOCl and HOCl, and 3 g.p.l. Na Cr O To this solution wasadded methanol in a ratio of approximately 1 part to 7 parts chlorate.36 N sulphuric acid was then added at a controlled feed rate in order toprevent too sudden a temperature rise and too large an excess of theformation of chlorine dioxide and/or chlorine. The temperature of thereaction was approximately C., and the pressure was at or aboutatmospheric.

It was found that fast pulping resulted (a Kappa Number of less than 10in less than 15 minutes) and that there was substantial bleaching (a GE.brightness above 60).

These results were achieved when a substantial excess (i.e. about 0.1 to2:0 molar excess) of reagent chemicals were used compared to therequirements for slow pulpinn. This resulted in chlorine dioxide and/orchlorine being present in the vapor phase above the pulping liquor. Suchbleaching agents are preferably drawn oil to be used in a second stage,or in several other stages for further bleaching and/or pulping.

Example H Example I was repeated, except that the temperature wasincreased to 120-130 C. The produced gases (C10, and/or C1 wereconstantly bled otf. Similar Kappa numbers and GE. Brightness numberswere achieved in a few minutes e.g. 2 minutes time.

It is observed that at such higher temperatures the unreacted methanolvaporized. Such vaporized methanol may be condensed and returned to thesystem.

Example III Example I was repeated except that the acid used was dilutesulphuric acid, of 6 N. The pulped product has substantially the samecharacteristics except that the reaction time was increased to about 10hours.

Examples IV, V and VI ture was necessary in order to avoid undigestedand discolored cores of the wood chips. The temperature shouldpreferably be less than 120 C. if the pH is below 2.

Examples VII-XII Example XIX Western Hemlock and Spruce Wood Chips wereimmersed in a solution containing g.p.l. of sodium chlorate acidified topH 2 with muriatic acid and then additional acid to an amount equal tothe stoichiometry ratio of HCl versus NaClO for production of two moleschlorine dioxide and one mole chlorine. The solution releases chlorinedioxide and chlorine when the temperature is raised above 30 C.

The pulp produced had a Kappa Number equal to 24 and GE. Brightness of54 after about two hours timeat 70 C. and 100 p.s.i.g. The amount ofbleaching agent was almost fully reacted in the pulping process and theamount of bleaching agent in the vapor phase was negligible. Theresidual chlorate in the treatment liquor was below 0.5 g.p.l.

Conventional bleaching sequences after the above pulping processresulted in fully bleached pulp 90 GE.

brightness and higher with minimum degradation of the pulp.

. Example XX Example XIX was repeated, but the reaction temperature wasincreased to 150 C. and pressure maintained was up to p.s.i.g. It wasfound that, for the same degree of pulping,.a significantly shortertreatment time,

i.e., about 45 minutes, was necessary. However, this re sulted in lowerpulp yields.

Examples XXI and XXII Examples XXIII and XXIV Examples XIX and XX wererepeated, except that the wood chips were subjected to a pre-steamtreatment. It was found that the amount of chemicals required werereduced.

Examples XXV and XXVI Examples XIX and XX were repeated, except that thewood chips were pre-treated with alkali. It was found that the amount ofchemicals was reduced.

Examples XXVII and XXVIII Examples XIX and XX were repeated, except thatthe wood chips 'were pre-treated with sulphur dioxide. The excesssulphur dioxide may be used as a reducing agent for the chlorate. It wasfound that the amount of chemicals required was reduced.

In any of the above twenty-eight examples, the treatment solution may beresaturated with chlorate and makeup acid added while .controlling thewater balance by means of released vapor. The solution in the pulp maythen be removed. Thus, the dissolved wood products could be concentratedand values recovered.

' The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1'. A process for the treatment of cellulosic materials in sub-dividedform, which process comprises the steps of:

(1) providing an enclosed reaction zone; (2) providing a reactant liquorphase in said reaction zone;

(3) providing a superposed gas phase over said reactant liquor in saidreaction zone; and

(4) agitating said subdivided cellulosic material in said enclosedreaction zone; wherein (a) said reactant liquor phase comprises anaqueous liquor comprising a water soluble chlorate and a reducing agentfor said chlorate, said reducing agent being present in 0.1 to 2.0.molarexcess, based on the amount of chlorate and (b) said gas phase containsevolved chlorine dioxide and/ or chlorine.

2. The process of claim 1 wherein the said agitation step (4) isconducted at a temperature of less than C., at a pressure betweenatmospheric and up to 11 atmospheres and at a pH of less than 4.

3. The process of claim 1 including the preliminary step of subjectingthe sub-divided cellulosic material to a steam pre-treatin-g step.

4. The process of claim 1 including the preliminary step of subjectingthe sub-divided cellulosic material to an alkali pretreating step.

5. The process of claim 1 including the preliminary step of subjectingthe sub-divided cellulosic material to a pretreatment with sulphurdioxide.

6. The process of claim 1 wherein said reducing agent is selected from agroup consisting of acetic acid, hydrochloric acid, sulfuric acid,phosphoric acid and nitric acid.

7. The process of claim 6 wherein said metal chlorate comprises sodiumchlorate andwherein said acid comprises hydrochloric acid.

8. The process of claim 7 wherein said agitation reaction (4) isconducted at a temperature of less than 150 C., at pressures betweenatmospheric and up to 11 atmospheres, and at a pH of less than 4.

9. The process of claim 1 wherein said reactant liquor phase comprisesan aqueous liquor comprising a water soluble metal chlorate, a watersoluble metal chloride, and an acid reducing agent for said chlorate,selected from the group consisting of acetic acid, hydrochloric acid,sulfuric acid, phosphoric acid and nitric acid.

10. The process of claim 9 wherein the metal chlorate comprises sodiumchlorate, wherein the metal chloride comprises sodium chloride andwherein the acid comprises sulfuric acid.

11. The process of claim 10 wherein said agitation reaction (4) isconducted at a temperature of less than 150 C., at pressures betweenatmospheric and up to 11 atmospheres, and at a pH of less than 4.

12. The process of claim 1 wherein said reactant liquor phase comprisesa water soluble chlorate, an organic reducing agent selected from thegroup consisting of oxalic acid and methanol, and an acid reducing agentfor said chlorate selected from a group consisting of acetic acid,oxalic acid, hydrochloric acid, sulfuric acid, phosphoric acid andnitric acid.

13. The process of claim 12 wherein the chlorate comprises hypochlorousacid, wherein the organic reducing agent comprises methanol and whereinthe acid reducing agent comprises sulfuric acid.

14. The process of claim 13 wherein said agitating step (4) is conductedat a temperature of less than 150 C., at pressures between atmosphericand up to 11 atmospheres, and at a-pH of less than 4.

15. The process of claim 1 wherein said reactant liquor phase comprisesan aqueous liquor comprising a water soluble metal chlorate, sulfurdioxide, and an acid reducing agent for said chlorate, selected from thegroup consisting of acetic acid, hydrochloric acid, sulfuric acid,phosphoric acid and nitric acid.

16. The process of claim 15 wherein the metal chlorate comprises sodiumchlorate and wherein the acid comprises sulfuric acid.

117. The process of claim 16 wherein said agitation step (4) isconducted at a temperature of 150 C. at pressures between atmospheric upto 11 atmospheres, and at a pH of less than 4.

.18. The process of claim 1 including the step of withdrawing excessgaseous chlorine dioxide and/or chlorine from the superposed gas phaseover said reactant liquor in said reaction zone.

19. The process of claim 9 including the step of withdrawing excessgaseous chlorine dioxide and/or chlorine from the superposed gas phaseover said reactant liquor in said reaction zone.

20. The process of claim 12 including the step of withdrawing excessgaseous chlorine dioxide and/or chlorine from the superposed gas phaseover said reactant liquor in said reaction zone.

21. The process of claim 15 including the step of withdrawing excessgaseous chlorine dioxide and/or chlorine from the superposed gas phaseover said reactant liquor in said reaction zone.

22. The process of claim 18 wherein the withdrawn gaseous chlorinedioxide and/ or chlorine is employed for further treatment of thecellulosic material.

References Cited UNITED STATES PATENTS 1,828,338 10/ 1931 Neumann 162-732,065,396 12/ 1936 Richter 162--64 2,203,205 6/ 1940 Rawling 162-882,730,426 1/ 1956 Becker 162-66 FOREIGN PATENTS 452,351 11/1948 Canada.

533,803 11/1956 Canada.

546,718 9/1957 Canada.

8. LEON BASHORE, Primary Examiner A. L. CORBIN, Assistant Examiner US.Cl. X.R.

